1. Field of the Invention
The present invention relates to a dry etching method for applying an etching treatment to a silicon semiconductor wafer.
2. Description of the Related Art
A dry etching treatment is applied to a silicon semiconductor wafer in the manufacture of a semiconductor device. For example, the dry etching treatment is employed for the separation of a capacitor or an element and for forming a contact hole. It is necessary to satisfy various requirements in the etching treatment. For example, the etching should be carried out with a large etching selectivity relative to a resist film or an undercoat film. It is also necessary for the side wall of a groove to be etched smoothly to provide a wall surface substantially perpendicular to the wafer surface. In other words, a high etching anisotropy should be satisfied. Further, the etching should be carried out with a high etching rate. Still further, it is important to diminish the etching residue.
It was customary to use, for example, a CCl.sub.4 gas in the dry etching treatment. In this case, an electric field is applied to the CCl.sub.4 gas so as to form a plasma. A film is removed by Cl contained in the plasma. On the other hand, carbon contained the plasma serves to form a protective film together with the organic component contained in a resist film and silicon so as to ensure an etching anisotropy. Further, the gas flow rate and power for applying an electric field to the gaseous atmosphere are suitably controlled so as to obtain conditions for achieving a high etching rate and etching selectivity.
In the conventional method, however, both a side wall-protecting function and a film-removing function are produced within a gas of a single kind so as to obtain an etching anisotropy. In this case, it is difficult to find optimum conditions under which these two different functions are produced satisfactorily. For example, if it is intended to intensify the side wall-protecting function, polymer is partly deposited on an unexpected portion as a residue.
What should also be noted is that the intensity of each of these functions is also changed by other conditions such as the power value, i.e., energy of plasma, with the result that it is very difficult to find optimum conditions which simultaneously permit a high etching rate, a satisfactory etching anisotropy, and a high etching selectivity.
For example, a high etching rate can be obtained by increasing the energy of the plasma. In this case, however, a sputtering function is produced unduly strongly, making it impossible to ensure a suitable etching selectivity relative to the undercoat layer. Thus, over-etching is brought about. By the contrary, the etching selectivity can be improved by diminishing the energy of the plasma. In this case, however, the etching rate is lowered. Also, if an oxide region is included in the surface of the film to be etched, the film-removing function is weakened, with the result that the oxide region is left unremoved as a columnar residue.
A measure for overcoming the difficulty noted above is proposed in, for example, U.S. Pat. No. 4,490,209. It is taught that a mixed gas prepared by mixing HBr and a chlorine-containing gas, e.g., HCl, at a predetermined ratio is used at a predetermined flow rate for etching a silicon layer. However, this U.S. Patent does not teach at all the criticalities of the other etching conditions.